1. Field of the Invention
The present invention relates to a read head with a high resistance soft magnetic flux guide layer for enhancing read sensor efficiency and, more particularly, to one or more high resistance soft magnetic flux guide layers that abut one or more end edges of the read sensor layer for increasing the magnetoresistive signal and/or for protecting the read sensor layer from direct exposure to the environment.
2. Description of Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly mounted on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent the ABS to cause the slider to ride on an air bearing a slight distance from the surface of the rotating disk. The write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A magnetic gap is formed between the first and second pole piece layers by a write gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field across the gap between the pole pieces. This field fringes across the gap at the ABS for the purpose of writing information in tracks on moving media, such as in circular tracks on a rotating disk.
The read head includes first and second shield layers, first and second gap layers, a read sensor and first and second lead layers that are connected to the read sensor for conducting a sense current through the read sensor. The first and second gap layers are located between the first and second shield layers and the read sensor and the first and second lead layers are located between the first and second gap layers. The distance between the first and second shield layers determines the linear read density of the read head. The read sensor has first and second side edges that define a track width of the read head. The product of the linear density and the track density equals the areal density of the read head which is the bit reading capability of the read head per square inch of the magnetic media.
The first and second leads abut the first and second edges of the read sensor in a connection which is referred to in the art as a contiguous junction. Each of the leads and the read sensor comprises a plurality of films. The read sensor can be a spin valve read sensor or an anisotropic magnetoresistive (AMR) read sensor. A spin valve read sensor typically includes a spacer film sandwiched between a free film and a pinned film. Adjacent the pinned film is a pinning film for pinning a magnetic moment of the pinned layer. The free layer has a magnetic moment that is free to rotate relative to the fixed magnetic moment of the pinned layer in response to field incursions from the rotating magnetic disk. This causes a change in resistance of the read sensor to the sense current that can be detected as potential changes by processing circuitry. Each lead typically includes a conductor film and one or more biasing films that bias the free film of the read sensor.
The free film is a soft magnetic material, such as Permalloy (NiFe). Magnetic incursions from the rotating magnetic disk rotate the magnetic moment of the free film. Unfortunately, magnetic spins in end portions of the free film are unstable. These magnetic spins are in domains that interface with each other along domain walls. When the free film is subjected to and then released from a magnetic field the domain walls do not return to their same orientation. This changes the magnetics of the free film and affects its performance. Accordingly, the end portions of the free film must be biased so that the magnetic spins in the end portions are directed parallel to the ABS in a single domain state. This biasing is accomplished by one of the aforementioned biasing films in each of the lead layers that abuts the first and second side edges of the read sensor and longitudinally biases the free layer parallel to the ABS.
The quality of the read sensor is rated by its change in resistance with respect to its resistance. The higher the ratio the better the read sensor. Unfortunately, upon the occurrence of a flux incursion from a rotating magnetic disk the field in the read sensor decays from a maximum at the ABS to zero at its back edge (stripe height). This decay reduces the ratio of the read sensor so that it is less efficient. In order to reduce this decay a flux guide layer has been located adjacent the back edge of the read sensor. A small amount of insulation is located between the edges of the read sensor and the flux guide layer so that the flux guide layer will not shunt the sense current. Unfortunately, this small amount of insulation seriously impacts a necessary magnetic path between the read sensor and the flux guide layer. For this reason flux guides have not been effective and therefore they have not been employed.